[Correlation between the stability of alpha-chymotrypsin at high temperatures and "salting in" of a strong solution]

A correlation was found between the thermal stability of alpha-chymotrypsin and the coefficient Ks of the Sechenov equation as a quantitative measure of the "salting-in" or "salting-out" capacity of solutes. At high temperatures, an increase in the concentration of "salting-in" agents (KSNC, GuHCl, urea, formamide) resulted in thermal stabilization of alpha-chymotrypsin. The maximal (about 100-fold) stabilizing effect in concentrated solutions of salting-in agents was comparable with those induced by covalent modification with hydrophilic reagents or immobilization. Conversely, an increase in the concentration of "salting-out" agents stabilized the enzyme only marginally at high temperatures. An additivity of solutes' action on the thermal stability of the protein has been demonstrated. The observed correlation was explained in terms of the solutes' action on the reversible conformational transition of the enzyme native form into a much more stable form existing at high temperatures.